Effect of phenolic acids and an aromatic aldehyde on infectivity of Meloidogyne javanica and colonization by Pseudomonas aeruginosa in mungbean

Abstract

Various concentrations of the two phenolic acids (benzoic acid and caffeic acid) used in combination caused greater suppression of the nematode population densities in soil and consequent root-knot development due to Me!oidogyne javanica in mungbean. With an increase in phenolic concentration, shoot growth was retarded progressively but there was no apparent effect on root growth. However, Pseudomonas aeruginosa to some extent reduced any adverse effect of the phenolic acids on plant growth. Combination of phenolic acids at higher concentrations also reduced populations of P. aeruginosa in the rhizosphere. Of the two phenolic acids tested, caffeic acid exhibited greater activity against M. javanica and was used with benzaldehyde, an aromatic aldehyde. Caffeic acid and benzaldehyde at high concentrations markedly suppressed nematode population densities and root-knot infestation. The two allelochemicals used with P. aeruginosa also significantly suppressed root-knot infection and enhanced plant growth. Benzaldehyde applied alone had no significant impact on populations of P. aerugil10sa whereas caffeic acid used alone or in combination with benzaldehyde markedly reduced bacterial populations.